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In-Depth Information
Scheme 2.2
from diethyl ether. Subsequently, the terphenyl diimine ligands
3a
-
c
are prepared
by boiling under reflux a solution of 2,3-butanedione and the amino compound in
benzene under the catalytic influence of
para
-toluenesulfonic acid. Increasing ster-
ic demand of the para-substituents requires longer reaction times to isolate the
products in good yields (61-85%). Complexes
4a
and
5a
are accessible by reaction
of
3a
with CODPdCl
2
at ambient temperature [27]. In contrast, the substituted ter-
phenyl ligands
3b
,
c
require the use of (PhCN)
2
PdCl
2
as precursor complex [28].
Interestingly, the sterically more demanding ligands
3b
,
c
were highly inefficient
in displacing the COD fragment effectively. Treatment of the dichloro complexes
(
4a
-
c
) with Sn(CH
3
)
4
afford the monomethyl compounds (Scheme 2.2,
5b
,
c
) [29].
2.2.2
Solid State Structures
The structures of the palladium dichloro compounds
4a
-
c
were determined by
single-crystal X-ray analysis. Compounds
4a
,
c
show disorder which could be re-
solved satisfactorily. The expected bidentate coordination of the diimine nitrogen
atoms to the Pd(II) center, forming square-planar (Fig. 2.6,
4a
,
b
) and distorted
square-planar (Fig. 2.6,
4c
) coordination environments, is found for all three com-
plexes (Tab. 2.1).
The phenyl rings in the 2,6-positions of the aniline moieties point towards each
other above and below the N-Pd-N plane as a consequence of the specific loca-
tion. In
4a
, the terphenyl units are not large enough to feel the steric influence of
its symmetry-related counterpart, leading to a complex architecture that is nearly
ideal
C
2v
-symmetric. However, already here, the aniline-phenyl rings lack a free
rotation around their N-C bond, as confirmed by variable temperature NMR ex-
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